The first equation is in the form of a quadratic equation, which can be solved by setting it equal to zero and factoring:

(35-x)x = 0
x(35-x) = 0
x = 0 or 35-x = 0
x = 0 or x = 35

Therefore, the solutions to the first equation are x = 0 and x = 35.

The second equation is a linear equation, which can be solved by isolating the variable:

9c - 21 = 9c + 18
Subtract 9c from both sides:
-21 = 18

This equation does not have a solution since -21 does not equal 18.